1. Field of the Invention
This invention relates to antennas and more particularly to a flat plate television antenna module.
2. Description of the Related Art
Television sets are often used in recreation vehicles, conversion vans, limousines and the like and such vehicles are typically equipped with an external television antenna. External antennas are of necessity kept small, and preferably encased in a streamlined housing, to reduce wind drag. This downsizing substantially lowers the efficiency of the antenna. The TV spectrum covers a large frequency span, down to 54 megahertz (MHz) at the low frequency end. A quarter-wavelength radiator and associated ground plane or a half-wave dipole is usually recommended for proper reception. However, at 54 MHz a quarter-wavelength is approximately 53 inches. An antenna of that size external to the vehicle is impractical due to the wind drag.
The reason for placing the antenna external to the vehicle, rather than internal is that the metallic vehicle structure prevents the proper reception of high frequency signals internal to the vehicle. In recent years, however, fiberglass has been used in the construction of the roof and other portions of many large trucks, recreational vehicles and other vehicles. Since fiberglass allows almost unaffected passage of high frequency signals, the television antenna can now be placed inside a vehicle.
Prior art TV antennas are typically of the dipole design with little or no radiation at the ends of the dipole. This creates an antenna which is highly directional. An annoying problem of such antennas in moving vehicles is that the level of the received signal changes as the direction of the vehicle changes, causing signal quality to fluctuate.
U.S. Pat. No. 5,402,134, issued Mar. 28, 1995 to Paul E. Miller et al., discloses a flat plat antenna module incorporating a mobile telephone antenna loop, an AM/FM antenna loop, and a CB antenna loop, which patent is incorporated by reference herein. A loop antenna of the type generally described in that patent does not require the metallic ground plane, is essentially an omnidirectional antenna and functions well in a fiberglass enclosure. However, such an antenna is not suitable for TV reception because of the bandwidth requirements of a TV antenna.